This invention relates to a process for making a closed-cell, alkenyl aromatic polymer foam structure having an enlarged average cell size.
Due to present environmental concerns over the use of potentially ozone-depleting flammable blowing agents it is desirable to make an alkenyl aromatic polymer foam structure with pristine blowing agents. Such pristine blowing agents typically include inorganic blowing agents such as carbon dioxide, nitrogen, water, argon, and the like.
A problem with using pristine blowing agents is maintaining desirable morphology in the resulting foam structure. One characteristic of the morphology is cell size. A desirable cell size can be difficult to maintain when using pristine (inorganic) blowing agents, particularly carbon dioxide, because of their relatively high nucleation and expansion rates.
Prior art attempts to make a foam structure having an enlarged cell size include the integration of a wax in a foam-forming gel prior to extrusion of the gel through a die to form the foam structure. Such use of a wax is seen in U.S. Pat. No. 4,229,396, which is incorporated herein by reference. Use of a wax may, however, create processing problems and physical property abherations in the foam structure. The wax may cause thermal stability variations or diminution in physical properties in the foam structure. The wax may also cause inconsistency in extrusion temperatures.
It would be desirable to make a foam structure with a blowing agent comprised partially or entirely of a pristine blowing agent with a desirable (enlarged) average cell size. It would further be desirable to make such foam structures with non-pristine blowing agents. It would further be desirable to make such foam structures while retaining desirable physical properties and thermal stability. It would be further desirable to make such foam structures without using a wax.